Unfortunately an even larger subset of the population doesn't need anonymity to act nasty to others, while their victims often need it to prevent it escalating. Google's attempts to force real names on Youtube comments to reduce spam and bad behavior have been... less than impressive in effect. In a lot of discussions if you force real names you ensure that those with the most to lose (and often the most at stake) are also the most vulnerable.

Even presuming that counter to actual experience the generic trolls are deterred by a real names policy, there are others who become a much bigger problem when they've got access to real identities. Why do you think doxing is considered such a big thing? SWATing, offline stalking, physical assault, etc. are all risks as soon as a harasser has your info. Even worse when you're talking about something like domestic violence support groups there's a very real danger of the abuser escalating if they discover the victim has been talking to other people. That's 2.1 million people in the US alone who report physical assault by a partner in a single year who could really use access to resources without revealing themselves.